There's a lib called xfixes? That's quite hilarious. Just read up on it and I think it's ok to include it. Would you like to create a pull request? That'll give you proper credit in the git commit list.

The hide the mouse for the whole screen is problematic and it's not how it works on other targets. People won't know how to close the window. Guess we need to build in some mechanism that automatically reverts the mouse-hide call when the mouse moves out of the window.

There is: "the X server reports EnterNotify or LeaveNotify events to clients who have selected for these events" if I can find where to receive this notification (I suspect Backends/System/Linux/.../System.cpp) then I can call show(true) and problem solved.